Delphi Direct Acting Piezo Injector Debuts on the Mercedes C250 CDI

1 December 2008

Delphi Direct Acting Diesel Common Rail System includes (clockwise from top left): DFI3 Piezo Injectors with Common Rail, Series 9 Modular Fuel Filter, DCM4 Light Duty Controller, and DFP3 High Pressure Pump. Click to enlarge.

Delphi Corporation’s new Direct Acting Piezo injector (earlier post) is making its debut in the new Direct Acting Diesel Common Rail System on the new Mercedes C250 CDI. In the new system, the injector needle is directly activated by a piezo ceramic actuator, removing the hydraulic circuit and its associated lag and energy consumption.

The piezo ceramic actuator directly operates the needle valve of the injector for initial lifts, such as those obtained in pilot injections, and a motion amplifier is used to help complete the lift for large injections. This enables the injector to spray fuel into the combustion chamber faster, with much improved spray momentum and accuracy, at higher pressures (up to 2,000 bar).

It also provides extremely fast opening and closing of the needle valve, independent of injection pressure. With needle velocities reaching above 3 m/s or 3 times faster than today’s servo systems, the system allows seven (or more) injection events per engine cycle. Delphi’s hydraulic circuit design makes best use of the characteristics of piezo ceramic actuators: high force and speed with efficient packaging.

With high-precision multiple injections of fuel, the fuel injection process can be adapted to all engine loads and speeds with greater accuracy, which has a positive impact on emissions, consumption and combustion noise. By offering the ability to control the needle opening rate electronically and independently of hydraulic constraints, the engine calibrator is able to satisfy the conflicting requirements of noise optimization and minimization of exhaust emissions without compromise.

At idle, the Direct Acting injector concept makes no perceptible noise above the engine itself.

The injector’s new operating principle is also completely leak free. No high-pressure fuel is wasted into a return flow back to the tank, saving up to 1 kW of lost energy used by today’s servo systems and removing the requirement of expensive fuel coolers even at a rail pressure of 2,000 bar.

Overall benefits include a considerable reduction in emissions, more torque and power across all engine speeds, and significantly improved fuel economy and refinement.

Mercedes-Benz’ completely-new four-cylinder diesel engine, named OM 651, made its debut in October at the Paris Motor Show on the C Class. (Earlier post.) Ultimately it will be produced in three versions: 150 kW, 125 kW and 100 kW, all with Delphi Diesel CR systems. The OM 651 is being launched first in its 150 kW version on the Mercedes C250 CDI BlueEFFICIENCY, marking the debut of Delphi’s Direct Acting Piezo CR system.

Mercedes-Benz subjected the engine and fuel injection system to 100,000 hours on test rig and 10,000,000 test kilometers under conditions ranging from the desert to Polar regions.

Delphi’s diesel technology was developed in Delphi diesel technical centers in Blois, France; Gillingham, United Kingdom; and Bascharage, Luxembourg.